Pneumatic suspension system for a vehicle

ABSTRACT

A pneumatic suspension system for a vehicle includes a compressed air accumulator, a compressed air transport device, at least one pneumatic bellows and an electrically controllable reversing valve used to connect the compressed air accumulator to a suction connection of the compressed air transport device, in order to increase the amount of air in the pneumatic bellows in a first switching position, and to connect an outlet connection of the compressed air transport device to the pneumatic bellows also used to connect the pneumatic bellows to the suction connection of the compressed air transport device and the outlet connection of the compressed air transport device to the pressure accumulators in a second switching position in order to reduce the amount of air in the pneumatic bellows. The reversing valve can be pre-controlled with the compressed air of the pneumatic suspension system.

BACKGROUND OF THE INVENTION

The present invention relates to an improved air-suspension system for avehicle, especially a closed or partly closed system.

An air-suspension system of the general type under consideration isdescribed in DE 199 59 556 C1.

In such conventional air-suspension systems, a compressed-air deliverydevice such as a compressor is used, on the one hand, to pump air asneeded from a compressed-air accumulator into the air-suspensionbellows, and, on the other hand, to pump air as needed from theair-suspension bellows back into the compressed-air accumulator. Tochange over between these two compressed-air delivery directions, achangeover-valve device is provided between the compressed-airaccumulator and air-suspension bellows on the one side and thecompressed-air delivery device on the other side. In the air-suspensionsystem described in DE 199 59 556 C1, the changeover-valve device cancomprise, for example, two electrically actuatable 3/2-way valvesdesigned as directly controlled solenoid valves.

In an air-suspension system, it is desired that the air-suspensionbellows can be filled and emptied as rapidly as possible. Thisnecessitates valve devices, and, in particular, also a changeover-valvedevice with large nominal width, or, in other words, with large passagecross section. Such valve devices have relatively large size and thusare relatively heavy and expensive.

SUMMARY OF THE INVENTION

Generally speaking, in accordance with the present invention, animproved vehicle air-suspension system is provided that permits rapidfilling and emptying of the air-suspension bellows with comparativelyinexpensive and compact construction.

The present invention has the advantage that the changeover-valvedevice, and, thus, also the air-suspension system, can be madelightweight and at a more favorable price than is possible withconventional solutions. A further advantage is that only a singleelectromagnet is necessary for electrical actuation. Moreover, it canhave relatively small dimensions. As a result, the electrical energyconsumption during actuation of the electromagnet is distinctly reducedcompared with conventional solutions. In addition, only a single controlconnection to an electronic control unit is needed for activation of thechangeover-valve device.

Still other objects and advantages of the present invention will in partbe obvious and will in part be apparent from the specification.

The present invention accordingly comprises the features ofconstruction, combination of elements, and arrangements of parts whichwill be exemplified in the construction hereinafter set forth, and thescope of the invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described in more detail hereinafter andfurther advantages will be pointed out on the basis of practicalexamples with reference to the accompanying drawings, wherein:

FIG. 1 is a schematic diagram of a partly closed air-suspension systemaccording to one embodiment of the present invention;

FIG. 2 shows a compressed-air delivery device for use in the inventiveair-suspension system according to FIG. 1;

FIG. 3 shows a 4/2-way changeover valve in a first operating position inaccordance with an embodiment of the present invention;

FIG. 4 shows the 4/2-way changeover valve in a second operating positionin accordance with an embodiment of the present invention;

FIG. 5 shows the 4/2-way valve in a third operating position inaccordance with an embodiment of the present invention;

FIGS. 6 to 9 show further embodiments of an air-discharge/dryer devicefor use in the inventive air-suspension system according to FIG. 1;

FIGS. 10 to 12 show further embodiments of a changeover-valve device foruse in the inventive air-suspension system according to FIG. 1;

FIGS. 13 and 14 show a 4/2-way changeover-valve device in differentvalve positions in accordance with an embodiment of the presentinvention.

In the figures, like reference symbols are used for parts thatcorrespond to one another.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The function of an air-suspension system for a vehicle is to adjust andcontrol, via leveling means, the level height of the vehicle bodyrelative to the vehicle axles and thus indirectly relative to theroadway. For this purpose such a leveling means is preferably disposedon each wheel of a vehicle, and air-suspension bellows are preferablyused as leveling means. By filling or venting the individualair-suspension bellows, any desired level heights of the vehicle bodycan be adjusted within an adjustment range provided for the purpose.Such air-suspension systems are preferably operated with compressed airas the pressurized medium.

In air-suspension systems constructed and arranged as open systems,compressed air is sucked in as necessary from the surroundings, or, inother words, from the atmosphere, and pumped into the air-suspensionbellows or into a compressed-air accumulator, or, in other words, areservoir tank. The compressed-air accumulator, however, is notabsolutely necessary and, depending on requirements, may even be leftout. During venting of the air-suspension bellows, the compressed-air isalways discharged directly to the atmosphere. Return delivery ofcompressed air from the air-suspension bellows into the compressed-airaccumulator is not provided in such cases. The open system is ofrelatively simple design, and operates with relatively few components.Such air-suspension systems have been used for many years in commercialvehicles such as trucks and buses and also in passenger cars.

In contrast, a closed system always contains a compressed-airaccumulator, which—at least theoretically—is filled one time withcompressed air, for example, during manufacture of the air-suspensionsystem. The closed system has no kind of communication with theatmosphere—at least theoretically. During operation as designed, thecompressed air is delivered forward and back as needed by acompressed-air delivery device, from the compressed-air accumulator tothe air-suspension bellows or from the air-suspension bellows to thecompressed-air accumulator. Compared with an open system, this has theadvantage that the change of pressure level to be established during airdelivery by the compressed-air delivery device, such as a compressor, isusually smaller, since the pressure of the compressed air to bedelivered is usually at a certain level, which is relatively highcompared with atmospheric pressure. As a result, the energy consumptionof such a closed system is smaller. In addition, the compressed-airdelivery device can be designed for smaller power consumption. Otheradvantages are that the compressed-air delivery device can be operatedwith a shorter “On” time and that it develops relatively little internalheat.

In practice, such closed systems are not able to function continuouslybecause they lose compressed air, for example due to leaks in theair-suspension bellows which are made of elastic material. It hastherefore been proposed that partly closed systems be used in which acompressed-air accumulator is also provided and in which, as long assufficient compressed air is present in the system, the compressed airis delivered forward and back between the compressed-air accumulator andthe air-suspension bellows, just as in the closed system. In addition,communication with the atmosphere is provided, so that the system can befilled with compressed air, for example in the event of pressure lossesor large temperature fluctuations, and air can be sucked in from theatmosphere. To avoid overpressure conditions, it is additionallystandard practice to provide an air-discharge device for venting excesspressure to the atmosphere.

In such a partly closed system, therefore, some air exchange, albeit oflimited extent, takes place with the atmosphere. As a result, the partlyclosed system not only is practical but also it can largely exploit theadvantages of a closed system. Such an air-suspension system designed asa partly closed system is preferably provided with the followingfunctional units:

-   -   a compressed-air delivery device, which preferably is designed        as a compressor and, for example, can be driven by an electric        motor,    -   a compressed-air accumulator for storage of compressed air at a        specified pressure level,    -   air-suspension bellows,    -   an air-intake device,    -   an air-discharge device, and    -   an air-dryer device.

The foregoing functional units can be placed in communication with oneanother via actuatable valve devices, especially electrically actuatablevalve devices, in such a way that “increase air quantity”, “hold airquantity” and “decrease air quantity” functions can be activated for theair-suspension bellows. A desired level height can then be adjusted forthe duration of an “increase air quantity” or “decrease air quantity”process. Such an air-suspension system is preferably controlled by anelectronic control unit.

FIG. 1 illustrates a partly closed air-suspension system according to apreferred embodiment of the present invention. The compressed-airdelivery device is illustrated in block (1), which is outlined in brokenlines. The air-discharge device in combination with the air-dryerdevice, referred to hereinafter as air-discharge/dryer device (2), isillustrated in block (2), which is outlined in broken lines. Theair-intake device is illustrated in block (4), which is outlined bybroken lines. The compressed-air accumulator (9) as well as theair-suspension bellows (64, 65, 66, 67) are also illustrated. Inaddition, displacement sensors (68, 69, 70, 71) are allocated toair-suspension bellows (64, 65, 66, 67). Via electrical lines,displacement sensors (68, 69, 70, 71) respectively transmit, to anelectronic control unit (5), an electrical signal representative of thelevel height of the vehicle body in the region of that air-suspensionbellows to which they are allocated.

In a further block (3), which is also outlined in broken lines, there isillustrated a changeover-valve device which is used for control of thecompressed-air flow direction during delivery of compressed air forwardor back between compressed-air accumulator (9) and air-suspensionbellows (64, 65, 66, 67). By switching changeover-valve device (3) to afirst valve position, compressed-air accumulator (9), acting as acompressed-air source, can be placed in communication alternately withcompressed-air bellows (64, 65, 66, 67). In a second valve position ofchangeover valve (3), air-suspension bellows (64, 65, 66, 67), acting asthe compressed-air source, can be placed in communication withcompressed-air accumulator (9). Accordingly, the “increase air quantity”function can be activated relative to air-suspension bellows (64, 65,66, 67) in the first valve position, while the “decrease air quantity”function can be activated in the second valve position.

Via a shutoff valve (8), designed as an electromagnetically actuatable2/2-way valve and also referred to hereinafter as the accumulator valve,compressed-air accumulator (9) illustrated in FIG. 1 is placed incommunication with a port (318) of changeover-valve device (3). Viarespective shutoff valves (60, 61, 62, 63) disposed upstream from eachair-suspension bellows and also referred to hereinafter as bellowsvalves, as well as via a common compressed-air line (72), air-suspensionbellows (64, 65, 66, 67) are placed in communication with a further port(316) of changeover-valve device (3). Preferably, bellows valves (60,61, 62, 63) are also designed as electromagnetically actuatable 2/2-wayvalves. Check valves (51, 52) connected via their inlet sides areprovided at a further port (317) of changeover-valve device (3). On theoutlet side, check valve (51) is in communication with air intake device(4) as well as with a suction port (105) of compressed-air deliverydevice (1). An outlet port (106) of compressed-air delivery device (1)is in communication with an air inlet of air-discharge/dryer device (2).A check valve (50) is disposed at one outlet of air-discharge/dryerdevice (2). Check valves (50, 52) are in communication via their outletsides with a further port (315) of changeover-valve device (3).

In the air-suspension system configuration illustrated in FIG. 1, thereis disposed, at the outlet side of check valve (50), a pressure sensor(7) that measures the pressure present there and transmits an electricalsignal representative of that pressure to electronic control unit (5).If necessary, pressure sensor (7) can be provided as an option or caneven be omitted to achieve more favorable manufacturing costs for theair-suspension system, as will be explained in more detail hereinafter.

There is also provided an electric motor (6) that can be turned on viaan electrical signal from electronic control unit (5). Via a drive shaft(14), electric motor (6) drives a piston machine (12) provided incompressed-air delivery device (1).

Electronic control unit (5) is preferably used for control of allfunctions of the air-suspension system. For this purpose, control unit(5) is connected via electrical lines to an electric actuating device ofchangeover-valve device (3), to shutoff valves (8, 60, 61, 62, 63), tooptional pressure sensor (7), to displacement sensors (68, 69, 70, 71)and to electric motor (6).

Compressed-air delivery device (1) is provided with the functional unitsexplained in greater detail hereinafter. A piston machine (12) is usedto deliver air from suction port (105) to outlet port (106) ofcompressed-air delivery device (1). Piston machine (12) can be designedas any suitable conventional piston compressor, even, for example, arocking-piston compressor. As mentioned, piston machine (12) can bedriven via a drive shaft (14). On the intake side of compressed-airdelivery device (1) there is disposed a suction valve (11) designed as acheck valve. On the outlet side of compressed-air delivery device (1)there is disposed an outlet valve (13), also designed as a check valve.The delivery direction of compressed-air delivery device (1) isdetermined by check valves (11, 13).

Hereinafter, not only the suction valve (11) but also all parts of theair-suspension system in direct or indirect pneumatic communication withsuction port (105), from suction valve (11) to port (317) ofchangeover-valve device (3), will be regarded as allocated to the intakeside of compressed-air delivery device (1). In the practical exampleaccording to FIG. 1, these are parts (10, 11, 40, 41, 42, 51, 105, 317)as well as the inlet of check valve (52). Also hereinafter, not only theoutlet valve (13) but also all parts of the air-suspension system indirect or indirect pneumatic communication with outlet port (106), fromoutlet valve (13) to port (315) of changeover-valve device (3), will beregarded as allocated to the outlet side of compressed-air deliverydevice (1). In the practical example according to FIG. 1, these areparts (2, 7, 13, 50, 106, 315) as well as the outlet of check valve(52).

As depicted in FIG. 1, the volume (10) illustrated with an accumulatorsymbol on the intake side of compressed-air delivery device (1)symbolically represents all volumes present on the intake side ofcompressed-air delivery device (1), such as the volume of the crankcaseof piston machine (12) or even the compressed-air lines connected to theintake side of compressed-air delivery device (1). Volumes present onthe outlet side of compressed-air delivery device (1) are representedcollectively by a volume (15), which will be described in more detailhereinafter, and which is illustrated in air-discharge/dryer device (2)in FIG. 1.

A practical example of such a compressed-air delivery device (1) isillustrated in FIG. 2 in the form of a piston compressor. The pistonmachine (12) is provided inside its case with a drive shaft (14), whichis mechanically connected to a piston (17) via a connecting member(104), a revolute joint (107), a connecting rod (16) and a furtherrevolute joint (18). In response to rotation of drive shaft (14), piston(17) executes an upward and downward movement. Piston (17) is equippedwith a circumferential seal (100), which seals a pressure space (108)provided above the piston from a suction space (110) provided in thecrankcase of compressor (12). On the top end of piston (17) there isdisposed suction valve (11), which for design reasons is preferablyformed as a thin plate, which is fastened to piston (17), for example bymeans of a screw (19). During upward movement of piston (17), suctionvalve (11) functions to seal pressure space (108) from an intake opening(101) that passes through piston (17).

Above pressure space (108) there is provided an outlet space (150). Inoutlet space (150) there is provided outlet valve (13), which for designreasons is preferably formed as a thin plate, which is fastened, forexample by means of a screw (103), to the underside of outlet space(150). During downward movement of piston (17), outlet valve (13) sealsoutlet space (150) from an outlet duct (102) as well as from pressurespace (108).

During a downward stroke of piston (17), the air sucked in via suctionport (105) flows through intake duct (101) and valve (11), which is openat the time, into pressure space (108), which at the time is shut offfrom outlet space (150) by means of valve (13). During an upward strokeof piston (17), suction valve (11) closes, whereby the air present inpressure space (108) is pressed through outlet duct (102) and outletvalve (13), which is open at the time, into outlet space (150). Fromoutlet space (150), the compressed air present there can then flow viaoutlet port (106) into downstream air-discharge/dryer device (2).

According to FIG. 1, air-discharge/dryer device (2) is provided in anadvantageous configuration with a compressed-air-controlled 4/3-wayvalve (20) as well as with an air dryer (21). Between 4/3-way valve (20)and air dryer (21) there is illustrated volume (15), represented by anaccumulator symbol, which represents the volumes due toair-discharge/dryer device (2), especially that due to the air-dryercartridge. The volumes present on the outlet side of compressed-airdelivery device (1) are also included in volume (15).

In the valve position of valve (20) illustrated in FIG. 1, thecompressed air discharged by compressed-air delivery device (1) flowsvia a compressed-air line (22) into valve (20) at a port (223), out ofvalve (20) at a further port (224) and into a compressed-air line (24),from there through air dryer (21) and from there via check valve (50) tochangeover-valve device (3). Via a compressed-air line (25), the outletside of air dryer (21) is additionally provided with communication backto a further port (225) of valve (20), which is shut off in the valveposition illustrated in FIG. 1. A further port (215) of valve (20) isused as the vent port of the air-suspension system; it is incommunication with the atmosphere.

Via a compressed-air line (23), port (223) of valve (20), which is incommunication with compressed-air delivery device (1), is incommunication with a compressed-air-actuated control port of valve (20).When the pressure at the control port rises appropriately, valve (20)can be changed over from the valve position illustrated in FIG. 1 to asecond and a third valve position.

The connecting duct between ports (223, 224) of valve (20) still hasrelatively large passage cross section in the first valve position, butin the second valve position it is changed over to a throttling positionwith greatly reduced passage cross section. Compressed-air line (25)continues to be shut off in the second valve position. As the pressureat the control port rises further, the third valve position is finallyestablished. The throttling position with greatly reduced passage crosssection is again provided between ports (223, 224) of valve (20).Compressed-air line (25) is then in communication with thecompressed-air outlet at port (215), or, in other words with theatmosphere, and so compressed air can be discharged to the atmosphere.In this context, valve (20) also functions as an overpressure safetyvalve, or, in other words, as a safeguard against undesirably highpressure values in the air-suspension system, as will also be describedin greater detail hereinafter.

Because of the throttling effect of valve (20) in the second and thirdvalve positions, the compressed air expands on its way fromcompressed-air line (22) to compressed-air line (24), and thus arrivesin expanded condition or, in other words, at a lower pressure level inair dryer (21), after which it can be discharged to the atmosphere whenthe third valve position of valve (20) is reached. Because of theexpansion of the compressed air as a result of the throttling effect, animproved regeneration effect of the dryer granules present in air dryer(21) is achieved. Thus a relatively good drying effect is achieved withrelatively little compressed-air consumption.

In contrast to conventional air-suspension systems, the air-dryer devicein the air-suspension system according to embodiments of the presentinvention described herein is advantageously disposed such thatcompressed air always flows through it in the same flow direction bothin normal operation of the air-suspension system and in regenerationoperation, or, in other words, during extraction of moisture from thedryer granules. This has the advantage that air dryer (21) can bemounted permanently at the outlet side of compressed-air delivery device(1). In particular, it can be disposed in relatively close spatialproximity to the compressed-air delivery device, and so air preheated bythe compressed-air delivery device can be passed through it in any modeof operation. Because of the spatially compact arrangement next to thecompressed-air delivery device, the heated compressed air can reach airdryer (21) with a relatively small temperature drop. Since hot air canabsorb the moisture much better than cold air, a further substantialimprovement of efficiency of regeneration of the dryer granules can beachieved by this configuration of the invention.

FIG. 3 shows air-discharge/dryer device (2) as described hereinabove,with an advantageously designed version of 4/3-way valve (20) in itsfirst valve position. Valve (20) has a housing (200), which in itsportion illustrated in the lower region of FIG. 3 is provided with alarger cross section than its other portions. As an example, housing(200) can be of rotationally symmetric construction. Inside housing(200) there is disposed a valve member (209) which is rigidly joined toa piston (205) provided for actuation of valve member (209). Piston(205) is guided in housing portion (207) and sealed in housing portion(207) via a circumferential seal (206). In the depressurized or almostdepressurized condition of valve (20) illustrated in FIG. 3, piston(205) is pressed against bottom (222) of housing (200) by a spring(208), which is braced against a pedestal-shaped region (221) of housing(200).

Annular seals (201, 202, 204), which are held in position by groovesdisposed in housing (200), are disposed at certain spacings in housing(200). Valve member (209) is provided with a wall (210), which is guidedinside seals (201, 202, 204) and can be displaced relative to seals(201, 202, 204) in response to a movement of piston (205). Housing (200)is provided with openings (223, 224, 225) to which the pressure lines(22, 24, 25) mentioned hereinabove are connected. Furthermore, anopening for vent port (215) is provided in the lower region of housing(200).

Wall (210) of valve member (209) is provided on the side facing opening(224) with an opening (212). This opening (212) has relatively smallcross section compared with the other flow cross sections of valve (20).As a result, a throttling effect, which is active in the second andthird valve position of valve (20), can be achieved during flow ofcompressed air through opening (212).

In the valve position of valve (20) illustrated in FIG. 3, acompressed-air flow injected via compressed-air line (22) can passthrough duct (213) into compressed-air line (24) and from there throughair dryer (21) to check valve (50). Flow of compressed air throughcompressed-air line (25) is prevented by seals (202, 204), or in otherwords compressed-air line (25) is shut off. According to the flowdirection indicated by arrow (23), the compressed air can also propagatethrough an opening (214) passing through piston (205) into the spacebounded by piston (205), housing underside (222) and seal (206).

When the pressure injected via compressed-air line (22) into valve (20)exceeds a certain minimum value, which also depends on the frictionbetween valve member (209) and seals (201, 202, 204) among otherfactors, piston (205) begins to move away from housing bottom (222)against the force of spring (208). Such a condition is illustrated inFIG. 4, where the pressure present in valve (20) has already reached amagnitude at which piston (205) has executed such a substantial movementagainst the force of spring (208) that valve (20) has occupied itssecond valve position.

In this second valve position, valve member (209) has reached seal(201), whereby duct (213) illustrated in FIG. 3 is shut off. Asindicated by arrow (216), a flow of compressed air from compressed-airline (22) to compressed-air line (24) now takes place through opening(212), which acts as a throttling point. As illustrated by arrow (23),compressed-air propagation continues to take place through opening(214), into the space bounded by piston (205), housing bottom (222) andseal (206). Compressed-air line (25) is still shut off.

As the pressure in valve (20) continues to rise, the third valveposition of valve (20) is occupied, as illustrated in FIG. 5. In thisvalve position, piston (205) bears against the upper side of housingregion (207). A compressed-air flow from compressed-air line (22) tocompressed-air line (24), as in the second valve position, continues totake place in throttled form through opening (212), as illustrated byarrow (216). The space that had previously been closed by seals (202,204) and that shuts off compressed-air line (25) is now opened relativeto seal (204), and so compressed air can flow out of compressed-air line(25) through opening (215) into the atmosphere, as illustrated by arrow(217).

An alternative embodiment of air-discharge/dryer device (2) isillustrated in FIG. 6. Instead of the 4/3-way valve described above, a4/2-way valve, or in other words a valve of simplified design with onlytwo valve positions, is utilized. As a result, valve (20) can be ofsimpler design and can be less expensive to manufacture.

In a further embodiment of the present invention, which is illustratedin FIG. 7, air-discharge/dryer device (2) can also be equipped with anelectromagnetically actuatable valve (20). Valve (20) according to FIG.7 is provided with an electromagnet (27) as actuating element instead ofwith pressurized-fluid actuating means. Electromagnet (27) can beconnected via an electrical line (26) to control unit (5).

In a further embodiment of the present invention according to FIG. 8,air-discharge/dryer device (2) is equipped with a pressure-controlledvalve device (220), which is disposed downstream from air dryer (21). Inaddition, a throttle (28) is disposed upstream from air dryer (21).Valve device (220) is designed as a 3/2-way valve, which is installed inthe compressed-air line connected to the pressure outlet of air dryer(21). As a result, a simple layout of the compressed-air lines on theoutlet side of air dryer is achieved(21).

FIG. 9 illustrates a further embodiment of air-discharge/dryer device(2) that, just as depicted in FIG. 8, provides a throttle (28) disposedupstream from air dryer (21) as well as a pressure-controlled valvedevice (29) disposed downstream from air dryer (21). Valve device (29)is designed as a 2/2-way valve. As a result, air-discharge/dryer device(2) can be manufactured particularly inexpensively. In an advantageouspractical implementation, the additional branch point of thecompressed-air lines illustrated according to FIG. 9 on the outlet sideof the air dryer can be integrated directly into valve device (29), andso the routing of the compressed-air lines is not more complicated thanthat of the configuration according to FIG. 8.

For rapid delivery of compressed air to the air-suspension bellows orfrom the air-suspension bellows, throttle (28) is designed in such a wayas to ensure that a compressed-air flow sufficient for the desiredrequirements can pass through throttle (28). On the other hand, toachieve an efficient regeneration effect for the dryer granules whilevalve device (29) is open, the passage cross section of valve device(29, 220) is larger than the passage cross section of throttle (28), inthe ratio, for example, of 4:1.

According to FIG. 1, there is proposed as changeover-valve device (3) anelectromagnetically actuatable multiway-valve arrangement that ispiloted by compressed air and comprises a pilot valve (31) and achangeover valve (30). Pilot valve (31) is designed as anelectromagnetically actuated 3/2-way valve that can be actuated bycontrol unit (5) via an electrical line. Changeover valve (30) isdesigned as a 4/2-way valve that can be actuated by compressed air andthat is in communication via compressed-air ports (315, 316, 317, 318)with the other parts of the air-suspension system. Via pilot valve (31),the compressed-air-actuatable control input of changeover valve (30) canbe placed optionally in communication with the pressure discharged bycompressed-air delivery device (1) via air-discharge/dryer device (2)and check valve (50), or with the atmosphere. To avoid undesirably highair consumption during actuation of changeover valve (30), the controlvolume of this valve is kept small. FIGS. 13 and 14 show a practicalexample of a changeover valve designed in this way having small controlvolume. Furthermore, it is advantageous to keep the changeover frequencylow by suitable control algorithms in control unit (5), in order tominimize the air consumption.

Compared with a 4/2-way changeover valve controlled directly by anelectromagnet, valve arrangement (3) with pilot valve as illustrated inFIG. 1 has the advantage that the actuating forces that are applied bythe electromagnet are smaller. As a result, the electromagnet can be ofsmaller and less expensive design. The fact that the pilot pressure isdrawn from the compressed-air outlet branch of compressed-air deliverydevice (1) has the advantage that changeover-valve device (3) isfunctional in every operating condition of the air-suspension system.For example, it is functional even during initial startup, whilecompressed-air accumulator (9) is still empty.

FIG. 10 illustrates an alternative construction of changeover-valvedevice (3) comprising a changeover valve (30) designed as a slide valvethat can be actuated by an electric motor plus an electric motor (32)that can be activated by control unit (5) in order to bring aboutactuation.

A further alternative embodiment of changeover-valve device (3) isillustrated in FIG. 11. Instead of a single changeover valve with4/2-way function, as explained on the basis of FIGS. 1 and 10, acombination of two pressure-controlled 3/2-way valves (33, 34), whichcan be actuated by pilot valve (31), can be utilized. As regards itscompressed-air port sides (35, 36), changeover-valve device (3)illustrated in FIG. 11 can be integrated as desired into theair-suspension system according to FIG. 1. In other words, it ispossible, for example, to place port side (35) in communication with thecompressed-air delivery device and port side (36) in communication withthe compressed-air accumulator or with the air-suspension bellows.Conversely, port side (36) can also be placed in communication with thecompressed-air delivery device, in which case port side (35) is placedin communication with the compressed-air accumulator and theair-suspension bellows.

A further embodiment of changeover-valve device (3) is indicated in FIG.12. Four pneumatically actuatable 2/2-way valves (37, 38, 39, 300),which can be actuated by pilot valve (31), are used for changeover. Asexplained on the basis of FIG. 11, the port sides (35, 36) ofchangeover-valve device (3) can also be connected as desired into theair-suspension system according to FIG. 1.

An advantageously designed configuration of changeover-valve device (3)illustrated in FIG. 1 will be hereinafter described on the basis ofFIGS. 13 and 14. FIG. 13 shows changeover-valve device (3) in unactuatedcondition and FIG. 14 shows it in actuated condition.

Changeover-valve device (3) comprises pilot valve (31) and changeovervalve (30). Pilot valve (31) is provided with an electromagnetarrangement (301, 302), which is designed as electrical coil (301) andan armature (302), which is disposed inside coil (301) and can be movedin longitudinal direction of coil (301). Armature (302) simultaneouslyfunctions as the valve-closing member. For application as thevalve-closing member, the armature is equipped at one of its end faceswith a seal (305) made of an elastomer and at its opposite end face witha further seal (306), also made of an elastomer. On its circumference,armature (302) is provided with grooves (307, 308) running inlongitudinal direction and functioning as air-guide ducts. Armature(302) is braced on a spring (304), which is disposed inside coil (301).Spring (304) in turn is braced on a valve closure element (309), whichcloses off pilot valve (31) at its upper end. Valve closure element(309) is equipped with a bore running along its longitudinal axis andfunctioning as pressure-outlet duct (303) for venting, to theatmosphere, the compressed air that can be injected by pilot valve (31)into changeover valve (30).

Pilot valve (31) is joined to changeover valve (30) to form a rigidunit. In the unactuated condition, as illustrated in FIG. 13, armature(302) is pressed by the force of spring (304) onto a valve seat (311)provided in changeover valve (30). In the process, seal (306) closes offvalve seat (311). In this condition, seal (305) is not in contact withvalve closure element (309), and so pressure outlet duct (303) is open.

Changeover valve (30) comprises a valve housing (319), which is providedwith various compressed-air ports (315, 316, 317, 318) as well asair-guide ducts (314, 312). Compressed-air port (315) functions as theport to the outlet side of compressed-air delivery device (1). In otherwords, on the basis of the diagram of FIG. 1, it functions as the portto the outlet sides of check valves (50, 52). Compressed-air port (317)functions as the port to the intake side of compressed-air deliverydevice (1). That is, according to FIG. 1, it functions as the port tothe inlet sides of check valves (51, 52). Compressed-air port (318)functions as the port of compressed-air accumulator (9) via accumulatorvalve (8). Compressed-air port (316) functions as the port ofair-suspension bellows (64, 65, 66, 67) via bellows valves (60, 61, 62,63).

Compressed air to be used for pilot action can flow via compressed-airduct (314) to pilot valve (31) or to armature (302). During actuation ofpilot valve (31), electric current is applied to move armature (302)against the force of spring (304) into the position illustrated in FIG.14. Thereupon, valve seat (311) is released, allowing compressed air toflow via chamber (310) and via compressed-air duct (312) into a pilotchamber (313). Pilot chamber (313) is bounded by a longitudinallymovable piston (320), which is urged by compressed air present in pilotchamber (313). Piston (320) is braced via a spring (321) against anopposing stop in valve housing (319). When appropriate compressed air isadmitted into chamber (313), piston (320) is moved against the force ofspring (321) into the position illustrated in FIG. 14. In the process, avalve slide (322) joined rigidly to piston (320) is moved therewith intothe position illustrated in FIG. 14.

Via valve slide (322), compressed-air ports (315, 316, 317, 318) areplaced in communication with one another in the way already explained onthe basis of FIG. 1. Thus, in the unactuated position ofchangeover-valve device (3) illustrated in FIG. 13, compressed-air port(315) is in communication with compressed-air port (318), andcompressed-air port (316) is in communication with compressed-air port(317). In the actuated case according to FIG. 14, compressed-air port(315) is in communication with compressed-air port (316), andcompressed-air port (317) is in communication with compressed-air port(318).

Air-intake device (4) is provided as a further functional unit inFIG. 1. It is provided with an air-intake port (42) in communicationwith the atmosphere, with a filter (41) for filtering out impurities ofthe ambient air and with a check valve (40). This type of embodiment ofair-intake device (4) has the advantage that, in the event of acorresponding air demand on the intake side of compressed-air deliverydevice (1), for example in the event that the pressure in compressed-airaccumulator (9) is too low or that valves (8, 60, 61, 62, 63) are shutoff during regeneration of the dryer granules, air is automatically andadequately sucked in from the atmosphere, since check valve (40) doesnot need any special control.

The air-suspension system described hereinabove can be operated in anumber of modes of operation, which will be described in greater detailhereinafter. In the process, a number of synergy effects, by which theair-suspension system can be used particularly efficiently, are obtainedin the air-suspension system illustrated in FIG. 1 as well as in theconfigurations according to FIGS. 2 to 14 described hereinabove.

The following modes of operation of the air-suspension system will bedescribed hereinafter:

1. “Neutral condition”: Referring to a basic condition of theair-suspension system, in which no compressed-air delivery orcompressed-air movement takes place between the individual components ofthe air-suspension system; this condition is active in particular in thevalve positions of the valves illustrated in FIG. 1 as well as whenelectric motor (6) is turned off.

2. “Increase”: Referring to an increase of the compressed-air quantityin one or more air-suspension bellows (64, 65, 66, 67).

3. “Decrease”: Referring to a decrease of the compressed-air quantity inone or more air-suspension bellows (64, 65, 66, 67).

4. “Low-pressure compensation”: Referring to compensation, by intake ofair from the atmosphere, for too-low air pressure or too-smallcompressed-air quantity, for example in compressed-air accumulator (9).

5. “Overpressure compensation”: Referring to compensation, by venting tothe atmosphere, for too-high air pressure or too-large compressed-airquantity in the air-suspension system, for example in compressed-airaccumulator (9).

6. “Regeneration”: Referring to regeneration of air dryer (21), or inother words removal of moisture stored in the dryer granules of airdryer (21), for which purpose air stored in the air-suspension system orsucked in from the atmosphere is vented through air dryer (21) to theatmosphere.

7. “Starting help”: Referring to assistance, by boosting with compressedair, for startup of compressed-air delivery device (1) or its electricmotor (6) used as the drive.

During the first startup of the air-suspension system according to FIG.1, and starting from the neutral condition, compressed-air accumulator(9) as well as air-suspension bellows (64, 65, 66, 67) are for the timebeing at a pressure level that corresponds to atmospheric pressure. Acompressed-air quantity adequate for the air-suspension system tofunction as designed is therefore not yet present in this condition.Control unit (5) recognizes this by evaluating the displacementinformation supplied by displacement sensors (68, 69, 70, 71). Ifpressure sensor (7) is also provided, control unit (5) additionallyrefers to the pressure information supplied by pressure sensor (7) torecognize the inadequate air quantity. In this condition, control unit(5) first activates the “Low-pressure compensation” mode of operation ofthe air-suspension system.

For this purpose, changeover-valve device (3) is used to establishcommunication between outlet port (106) of compressed-air deliverydevice (1) and air-suspension bellows (64, 65, 66, 67). As a result,compressed-air accumulator (9) is simultaneously placed in communicationwith the intake side of compressed-air delivery device (1). In addition,accumulator valve (8) and bellows valves (60, 61, 62, 63) are switchedto open position. Electric motor (6) is then turned on, whereuponcompressed-air delivery device (1) begins to deliver compressed air.Since no notable air quantity can be sucked in from the branch—incommunication with compressed-air accumulator (9)—of the compressed-airline on the intake side of compressed-air delivery device (1), a reducedpressure relative to atmospheric pressure then develops on the intakeside, causing check valve (40) to open. As a result, compressed-airdelivery device (1) is able to suck in air from the atmosphere via airintake device (4). The sucked-in air is discharged on the outlet side ofcompressed-air delivery device (1), where it flows viaair-discharge/dryer device (2), check valve (50), changeover-valvedevice (3) and bellows valves (60, 61, 62, 63) into air-suspensionbellows (64, 65, 66, 67).

In the process, the resulting level height is monitored via displacementsensors (68, 69, 70, 71) by control unit (5). When a desired levelheight is reached at one of air-suspension bellows (64, 65, 66, 67),control unit (5) switches the bellows valve (60, 61, 62, 63) upstreamfrom that air-suspension bellows into shut-off position. When allbellows valves (60, 61, 62, 63) have been switched to shut-off positionin this way, control unit (5) turns electric motor (6) off and switchesaccumulator valve (8) into shut-off position; and the process of fillingof air-suspension bellows (64, 65, 66, 67) is complete.

Besides filling of air-suspension bellows (64, 65, 66, 67), it may beappropriate, during startup of the air-suspension system, also to fillcompressed-air accumulator (9), which initially is at atmosphericpressure. For this purpose, communication between outlet port (106) ofcompressed-air delivery device (1) and compressed-air accumulator (9) isestablished by means of changeover-valve device (3). Accumulator valve(8) is switched into open position while bellows valves (60, 61, 62, 63)are left in shut-off position. Electric motor (6) is then turned on,whereupon compressed-air delivery device (1) begins to delivercompressed air. Compressed-air delivery device (1) then sucks in airfrom the atmosphere through air-intake device (4). The sucked-in air isdischarged on the outlet side of compressed-air delivery device (1),where it flows via air-discharge/dryer device (2), check valve (50),changeover-valve device (3) and accumulator valve (8) intocompressed-air accumulator (9).

This process of filling compressed-air accumulator (9) can take placeunder time control, for example. That is, electric motor (6) is turnedon for a predetermined filling-time interval. If pressure sensor (7) isprovided, the resulting pressure level is monitored via pressure sensor(7) by control unit (5). After the predetermined filling-time intervalhas elapsed, or when a desired pressure value has been reached, controlunit (5) turns electric motor (6) off once again and also switchesaccumulator valve (8) to shut-off position; and the process of fillingcompressed-air accumulator (9) is complete.

The process of filling explained above, that is, the “Low-pressurecompensation” mode of operation, is also activated automatically bycontrol unit (5) in subsequent operation of the air-suspension system ifan insufficient air quantity in the air-suspension system is suspectedon the basis of the signals of sensors (7, 68, 69, 70, 71).

In subsequent operation, that is, after compressed-air accumulator (9)and air-suspension bellows (64, 65, 66, 67) have been filled for thefirst time, the low-pressure condition described above may develop, forexample due to leaks in parts of the air-suspension system or even dueto operation of the air-suspension system under altered climaticconditions, such as lower ambient temperatures. Thus, it is necessary,for example, to refill compressed air into a compressed-air accumulator(9) that had been filled to a desired nominal pressure at high ambienttemperature if the vehicle equipped with the air-suspension system isbeing operated in a region with cooler ambient temperatures. Controlunit (5) automatically recognizes such a low-pressure condition byregular evaluation of the signals of sensors (7, 68, 69, 70, 71), and insuch a case automatically activates the “Low-pressure compensation” modeof operation.

In the case of a vehicle that was originally operated in a coolerclimatic region, it may be that the air quantity in the air-suspensionsystem is too large for operation in a hotter climatic region. As aresult, the pressure in compressed-air accumulator (9) will be above adesired or permissible limit value. In such a case, the “Overpressurecompensation” mode of operation is activated.

For this purpose, control unit (5), by means of changeover-valve device(3), places compressed-air accumulator (9) in communication with theintake side of compressed-air delivery device (1). To dissipate theoverpressure, accumulator valve (8) can now be opened to pass compressedair from compressed-air accumulator (9) via accumulator valve (8),changeover-valve device (3), check valve (51) and compressed-airdelivery device (1) to air-discharge/dryer device (2). By virtue ofcheck valve (40), the compressed air cannot escape via air-intake device(4) under these conditions, but instead it flows through check valves(11, 13), which open automatically in flow direction, and throughcompressed-air delivery device (1) without the need for electric motor(6) to be turned on. In air-discharge/dryer device (2), the arrivingoverpressure causes valve (20) to change over to its third valveposition, thus allowing the compressed air to flow further through valve(20), compressed-air line (24), air dryer (21), compressed-air line (25)and again through valve (20) and vent port (215) into the atmosphere. Inthis condition, no air flows via check valve (50), since bellows valves(60, 61, 62, 63), which in this operating condition are in communicationwith check valve (50) via changeover-valve device (3), are all inshut-off position.

The “Overpressure compensation” condition can be maintained, forexample, until the overpressure has been sufficiently dissipated thatvalve (20) automatically returns to its second valve position. In thiscase the overpressure is controlled and limited by suitable coordinationof the compressed-air actuation of valve (20) and restoring spring(208), or in other words by appropriate choice of the active area ofpiston (205) and of the force of spring (208).

As is evident from the foregoing, a suitable pressure range can beadjusted and maintained in the air-suspension system quasi-automaticallyeven without use of pressure sensor (7), since on the one hand checkvalve (40) automatically opens at corresponding low pressure and thusenables intake of air from the atmosphere, and on the other hand valve(20) automatically opens at corresponding overpressure and permits theexcess air to flow out into the atmosphere.

The air-suspension system is therefore functional even without pressuresensor (7). Thus, for cost reasons, for example, it is possible tomanage without this pressure sensor. Nevertheless, if a pressure sensor(7) is provided, a further advantage is achieved in that theair-suspension system is able to continue operating safely even in theevent of a defect or failure of pressure sensor (7).

In an air-suspension system without pressure sensor (7), for example,inadmissible overpressure in compressed-air accumulator (9) can bereliably prevented by placing compressed-air accumulator (9) incommunication with valve (20), which functions as the overpressuresafeguard, at regular time intervals, such as every 30 minutes.

If pressure sensor (7) is used, it is possible to implement furthercontrol algorithms, which can be provided as the control program incontrol unit (5) and by which further advantages can be achieved incontrol of the air-suspension system.

When pressure sensor (7) is present, control unit (5), in anadvantageous configuration of the invention, performs regular monitoringof the pressure in compressed-air accumulator (9). For this purpose,control unit (5) places compressed-air accumulator (9) in communicationwith pressure sensor (7) by actuating accumulator valve (8) andchangeover-valve device (3). In the process, compressed air is preventedby check valves (50, 52) from propagating undesirably fromcompressed-air accumulator (9) into other branches of the air-suspensionsystem. If control unit (5) detects, during such a regular check, thatthe pressure in compressed-air accumulator (9) has exceeded a desiredlimit value, control unit (5) activates the “Overpressure compensation”mode of operation.

In addition, it is advantageous to provide control unit (5) with theability to check and set the air pressure to be limited. For thispurpose, control unit (5) interrupts the previously describedoverpressure venting via valve (20) at predetermined time intervals bytoggling changeover-valve device (3) in such a way that communication isagain established between pressure sensor (7) and compressed-airaccumulator (9), so that the residual air pressure in the compressed-airaccumulator can be measured. If a limit value stored in control unit (5)is exceeded by the measured pressure value, control unit (5) thentoggles changeover-valve device (3) once again, so that furtheroverpressure dissipation can take place via valve (20). Otherwisecontrol unit (5) deactivates the “Overpressure compensation” mode ofoperation and reactivates the “Neutral condition” mode of operation.

In another advantageous embodiment of the present invention, controlunit (5) additionally tests the pressure values present inair-suspension bellows (64, 65, 66, 67) at certain time intervals byplacing one of the air-suspension bellows (64, 65, 66, 67) incommunication with pressure sensor (7) by appropriate control ofchangeover-valve device (3) and of shutoff valves (8, 60, 61, 62, 63).The measured pressure values of air-suspension bellows (64, 65, 66, 67)and of compressed-air accumulator (9) are stored in control unit (5).

If considerable differences develop between the pressure level incompressed-air accumulator (9) on the one hand and the pressure levelsin air-suspension bellows (64, 65, 66, 67) on the other hand, they canbe detected by control unit (5) on the basis of the stored pressurevalues, and so suitable corrective actions can be initiated. Forexample, a large pressure difference between compressed-air accumulator(9) and air-suspension bellows (64, 65, 66, 67) during delivery from thelow to the high pressure level would lead to a relatively long On timeof compressed-air delivery device (1). In an advantageous configuration,the On time can be shortened by programming control unit (5) in such away that the pressure difference is limited to a predetermined value.

If the pressure level of compressed-air accumulator (9) were to exceedthat of air-suspension bellows (64, 65, 66, 67) by more than thepredetermined value, control unit (5) switches the air-suspension systeminto the “Overpressure compensation” mode of operation. At the sametime, control unit (5) additionally turns on electric motor (6) in orderto operate compressed-air delivery device (1) for a predetermined time.As a result, a specified quantity of air is pumped via valve (20) intothe atmosphere. After the predetermined time has elapsed, control unit(5) turns compressed-air delivery device (1) off once again and thenrechecks the pressure present in compressed-air accumulator (9).

Conversely, if the pressure level of compressed-air accumulator (9) isbelow that of air-suspension bellows (64, 65, 66, 67) by more than thepredetermined value, control unit (5) switches the air-suspension systeminto the “Low-pressure compensation” mode of operation. As a result, airis sucked in from the atmosphere via air-intake device (4) and pumpedinto compressed-air accumulator (9). When a desired pressure value hasbeen reached, control unit (5) switches the air-suspension system backto the “Neutral condition” mode of operation.

During the further operation of the air-suspension system, control unit(5) checks, on the basis of the signals of displacement sensors (68, 69,70, 71), whether the level height of the vehicle body relative to thevehicle wheels or roadway corresponds to a desired index value. Thisindex value can be selected automatically by control unit (5) from aplurality of predetermined index values or index-value functions, forexample as a function of the driving situation. A predetermined indexvalue can also be provided by manual intervention, for example by thedriver. If a value below the respective index value is determined forone or more of the signals of displacement sensors (68, 69, 70, 71), itindicates a need for the vehicle body to be raised at the correspondingair-suspension bellows. Thus, the corresponding air-suspension bellowsare filled with additional compressed air. Hereinafter it will beassumed that this is necessary for air-suspension bellows (64).

Control unit (5) then activates the “Increase” mode of operation of theair-suspension system. In the process, compressed-air accumulator (9) isplaced in communication with changeover-valve device (3) by switchingaccumulator valve (8) to open position. Changeover-valve device (3) isswitched in such a way that compressed-air accumulator (9) is placed incommunication with the intake side of compressed-air delivery device(1). As a result, the outlet side of compressed-air delivery device (1)is simultaneously placed in communication with bellows valves (60, 61,62, 63). Furthermore, control unit (5) switches bellows valve (60) toopen position. If the pressure level in compressed-air accumulator (9)is higher than in air-suspension bellows (64), the compressed airalready flows directly via check valve (52) and additionally throughcompressed-air delivery device (1) into air-suspension bellows (64) evenif compressed-air delivery device (1) is stationary. In other words, bymeans of check valve (52), compressed-air delivery device (1) can becircumvented in the manner of a bypass. By virtue of the directcommunication via check valve (52), the flow resistance achieved issmaller and thus more favorable. In the process, control unit (5)monitors the filling of air-suspension bellows (64) on the basis of thepressure signal transmitted by pressure sensor (7), if it is present,and of the displacement signal transmitted by displacement sensor (68).As soon as the desired index value of level height has been reached atair-suspension bellows (64), control unit (5) switches accumulator valve(8) and bellows valve (60) to shut-off position.

To accelerate the flow process, or if control unit (5) does not detectany change in the value measured by displacement sensor (68), controlunit (5) turns on electric motor (6) to boost the delivery of air,whereby compressed-air delivery device (1) begins to operate. This isnecessary in particular if the pressure in compressed-air accumulator(9) is lower than or at best equal to the pressure in air-suspensionbellows (64) to be filled, or if filling of the air-suspension bellowsis to be accelerated. When compressed-air delivery device (1) begins tooperate, the delivered air flows via check valve (51), compressed-airdelivery device (1), air-discharge/dryer device (2) and check valve (50)into air-suspension bellows (64).

If the pressure on the outlet side of compressed-air delivery device(1), especially in volume (15), were to be lower than in air-suspensionbellows (64) to be filled, for example at the beginning of the“Increase” mode of operation, undesired lowering of the level height atthis air-suspension bellows (64) due to pressure equalization betweenair-suspension bellows (64) and volume (15) is prevented by check valve(50). For this purpose, check valve (50) is advantageously disposed asclosely as possible to changeover-valve device (3), in order to minimizeequalization processes via the compressed-air lines.

If, during delivery of air from compressed-air accumulator (9) bycompressed-air delivery device (1), it were to occur that thecompressed-air quantity present in compressed-air accumulator (9) is notadequate for filling air-suspension bellows (64), which is being treatedas the example, the air pressure on the intake side of compressed-airdelivery device (1) would drop below atmospheric pressure, whereby checkvalve (40) of air intake device (4) would automatically open. As aresult, compressed-air delivery device (1) can suck in the necessary airfrom the atmosphere automatically and without further actions by controlunit (5), and thus supply the necessary air quantity in air-suspensionbellows (64).

Conversely, if displacement sensor (68) indicates that the level heightis above the index value, air-suspension bellows (64) is vented. Controlunit (5) then activates the “Decrease” mode of operation of theair-suspension system. In the process, accumulator valve (8) and bellowsvalve (60) are switched to open position. Moreover, changeover-valvedevice (3) is switched in such a way that air-suspension bellows (64) isplaced in communication with the intake side of compressed-air deliverydevice (1) and compressed-air accumulator (9) is placed in communicationwith the outlet side of compressed-air delivery device (1). If the airpressure in air-suspension bellows (64) is higher than the air pressurein compressed-air accumulator (9), compressed air flows directly viacheck valve (52) and additionally via compressed-air delivery device (1)from air-suspension bellows (64) into compressed-air accumulator (9).Compressed-air delivery device (1) does not have to be actuated duringthat process. By analogy with the “Increase” mode of operation, controlunit (5) monitors the venting of air-suspension bellows (64) via sensors(7, 68). When the desired level height according to the index value hasbeen reached in air-suspension bellows (64), control unit (5) ends the“Decrease” mode of operation by switching accumulator valve (8) andbellows valve (60) to shut-off position.

To accelerate the flow process, or if control unit (5) does not detectany change in the value measured by displacement sensor (68), controlunit (5) turns on electric motor (6) to boost the delivery of air,whereby compressed-air delivery device (1) begins to operate. This isnecessary in particular if the pressure in air-suspension bellows (64)to be emptied is lower than or at best equal to the pressure incompressed-air accumulator (9), or if emptying of the air-suspensionbellows is to be accelerated. In this mode of operation, intake of airfrom the atmosphere via air-intake device (4) is not an option.Compressed-air delivery device (1) therefore sucks in air fromair-suspension bellows (64) via bellows valve (60), changeover-valvedevice (3) and check valve (51), and delivers it via air-discharge/dryerdevice (2), check valve (50), changeover-valve device (3) andaccumulator valve (8) into compressed-air accumulator (9).

If the pressure value present in compressed-air accumulator (9) isalready adequate or even above a desired limit value, valve (20), whichfunctions as the overpressure safeguard, automatically responds andswitches to its third valve position, so that the compressed airdelivered by compressed-air delivery device (1) is vented to theatmosphere. Independently of this automatic overpressure safeguard viavalve (20), control unit (5) can also prevent further delivery ofcompressed air into compressed-air accumulator (9) if a predeterminedpressure value—checked on the basis of the signal of pressure sensor(7)—stored in control unit (5) is reached in compressed-air accumulator(9). For this purpose, control unit (5) switches accumulator valve (8)to shut-off position. The compressed air subsequently delivered bycompressed-air delivery device (1) is then vented to the atmosphere viavalve (20) in response to a rapidly rising pressure at the outletside—which is shut off from compressed-air accumulator (9)—ofcompressed-air delivery device (1).

If the pressure on the intake side of compressed-air delivery device(1), especially in volume (10), is higher than in air-suspension bellows(64) to be vented, for example at the beginning of the “Decrease” modeof operation, undesired raising of the level height at thisair-suspension bellows (64) due to pressure equalization betweenair-suspension bellows (64) and volume (10) is prevented by check valve(51). For this purpose, check valve (51) is advantageously disposed asclosely as possible to changeover-valve device (3), in order to minimizeequalization processes via the compressed-air lines.

A typical magnitude for volume (10) in air-suspension systems forpassenger cars is around 0.5 liter and for volume (15) is around 0.4liter. By using check valves (50, 51), it is possible to avoid a complexdesign for minimizing the volume in compressed-air delivery device (1),in the electric motor (6) that is frequently integrated structurallyinto compressed-air delivery device (1), and in air-discharge/dryerdevice (2). Instead, the design can be selectively optimized from theviewpoint of costs.

The “Regeneration” mode of operation is used for regeneration of thedryer granules provided in air dryer (21), or in other words extractionof moisture therefrom. For this purpose, control unit (5) switchesaccumulator valve (8) and bellows valves (60, 61, 62, 63) to shut-offposition and turns on electric motor (6) to cause compressed-airdelivery device (1) to begin operating. Compressed-air delivery device(1) then sucks in air from the atmosphere via air-intake device (4) anddischarges this air in compressed condition on the outlet side, thecompressed air being heated compared with the ambient temperature. Assoon as the air pressure, which is rising on the outlet side, reachespredetermined values in this process, valve (20) switches from the firstvalve position, firstly to the second valve position and finally to thethird valve position. In the third valve position, the compressed airflows from compressed-air line (22) into compressed-air line (24), whilebeing throttled by valve (20). That is, the compressed air expands to alower pressure level than the pressure level present in compressed-airline (22). Air-discharge/dryer device (2) is preferably disposed inrelatively close spatial proximity to compressed-air delivery device(1), so that the heated compressed air arrives in air dryer (21) withoutsubstantial drop of temperature. The air expanded and additionallyheated in this way has relatively high moisture-absorption potential,and so the compressed air flowing from air dryer (21) intocompressed-air line (25) has a relatively high moisture content. Thisair is then vented through valve (20) into the atmosphere. As a result,there is achieved very efficient and rapid drying of the dryer granules.

Otherwise, regeneration of the dryer granules is also performed wheneverthe already explained “Overpressure compensation” mode of operation isactivated, or in other words whenever surplus compressed air stored incompressed-air accumulator (9), for example, is being dissipated viavalve (20). In this case, intake of air from the atmosphere is notnecessary.

In a preferred configuration of the invention, which can be used inparticular in an air-suspension system without pressure sensor (7), the“Regeneration” mode of operation is always activated automatically bycontrol unit (5) subsequent to one of the other modes of operation ifcompressed-air delivery device (1) had been in operation at the time. Inthis case, control unit (5) activates the “Regeneration” mode ofoperation in the sense of coasting down. In other words, when apreceding mode of operation such as “Increase” is ended, accumulatorvalve (8) and bellows valves (60, 61, 62, 63) are switched to shut-offposition but electric motor (6) is not turned off immediately. Instead,it is left running for a coast-down period. As a result, compressed-airdelivery device (1) continues to run and builds up an overpressure onthe outlet side. The air at overpressure then escapes via valve (20) andair dryer (21), thus achieving regeneration of the dryer granules. Afterthe predetermined coast-down period, such as, for example, 5 seconds,has elapsed, control unit (5) turns off electric motor (6), whereby theair-suspension system changes from the “Regeneration” mode of operationto the “Normal condition” mode of operation. As a result, it is ensuredthat the dryer granules have adequate absorption capacity for moistureat any time.

As indicated above, the compressed air always flows through air dryer(21) in the same flow direction in all modes of operation of theair-suspension system. As a result, it is possible to position checkvalve (50) in the compressed-air line between air-discharge/dryer device(2) and changeover-valve device (3) in such a way that check valve (50)is disposed relatively closely to changeover-valve device (3), andspecifically downstream from air-discharge/dryer device (2). This hasthe advantage that, during the “Increase” mode of operation, undesiredlowering of the level height as a result of pressure equalizationbetween volume (15) and the air-suspension bellows can be preventedparticularly effectively. On the other hand, if the air-drying conceptused were to be such that, during regeneration operation, compressed-airflows through air dryer (21) in the flow direction opposite to thatduring delivery of compressed air by compressed-air delivery device (1),as is known from DE 199 59 556 C1, check valve (50) would have to bedisposed between compressed-air delivery device (1) andair-discharge/dryer device (2) in the air-suspension system according toFIG. 1. In this case, however, check valve (50) could not preventpressure equalization processes between the volumes present inair-discharge/dryer device (2) and the air-suspension bellows. Theconsequence would be that undesired lowering of the level height causedby pressure equalization can take place in the “Increase” mode ofoperation.

From the fact that compressed air always flows in the same flowdirection through air-discharge/dryer device (2) and that consequentlycheck valve (50) is disposed in the compressed-air line betweenair-discharge/dryer device (2) and changeover-valve device (3), there isderived the further advantage that, during dissipation of anoverpressure in the “Overpressure compensation” mode of operation, theair cannot escape into the atmosphere without flowing through air dryer(21), since check valve (50) prevents it from doing so. As a result, allcompressed air vented into the atmosphere benefits regeneration of thedryer granules.

In addition, control unit (5) can be provided with the capability, inthe form, for example, of a subroutine of a control program executed incontrol unit (5), of switching the air-suspension system to“Regeneration” mode of operation if high moisture density is present inthe air-suspension system. For this purpose there can be provided, formeasuring the moisture content of the air in the air-suspension system,an additional moisture sensor that transmits a signal representative ofthe moisture content of the air to control unit (5).

Finally, the air-suspension system can also be operated in the “Startinghelp” mode of operation. This mode of operation is needed whenever thedrive power that can be applied by electric motor (6) fails to causecompressor (12) to start. This can occur, for example, in the presenceof relatively high backpressure on the outlet side, or in other words inoutlet space (150) of compressor (12), especially if piston (17) islocated at a position approximately midway between the two dead centers.

In an advantageous configuration of the present invention, which can beemployed in particular for an air-suspension system without pressuresensor (7), accumulator valve (8) is first opened and changeover-valvedevice (3) is toggled for a brief time, or in other words is operated ineach of the two valve positions. These actions take place beforeelectric motor (6) is started. As a result, pressure equalization isestablished between the intake side and outlet side of compressed-airdelivery device (1). Thereupon electric motor (6) is started.

In a further advantageous configuration, control unit (5) recognizes astarting-help demand by periodically monitoring the pressure valuesmeasured by means of pressure sensor (7), by evaluating the storedpressure values of compressed-air accumulator (9) and of theair-suspension bellows or by monitoring the current drawn by electricmotor (6). If a starting-help demand is recognized, control unit (5), byappropriate operation of changeover-valve device (3) and of shutoffvalves (8, 60, 61, 62, 63), places either compressed-air accumulator (9)or an air-suspension bellows having relatively high air pressure incommunication with the intake side of compressed-air delivery device(1). As a result, piston (17) of compressor (12) is urged by pressurefrom its underside, thus reducing the drive power that is necessary forstarting compressor (12) and that is supplied by electric motor (6).When compressor (12) has started, it is possible to switch back to thedesired mode of operation of the air suspension system.

It will thus be seen that the objects set forth above, among those madeapparent from the preceding description, are efficiently attained, andsince certain changes may be made in the above constructions withoutdeparting from the spirit and scope of the invention, it is intendedthat all matter contained in the above description or shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed and all statements of the scope of the invention which, as amatter of language, might be said to fall therebetween.

1. An air-suspension system for a vehicle, comprising a compressed-airaccumulator, a compressed-air delivery device, at least oneair-suspension bellows and an electrically activatable changeover-valvedevice, said electrically activatable changeover-valve device beingswitchable to (i) a first valve position to increase air quantity insaid at least one air-suspension bellows, by placing compressed-airaccumulator in communication with a suction port of said compressed-airdelivery device and an outlet port of said compressed-air deliverydevice in communication with said at least one compressed-air bellows,and (ii) a second valve position to decrease air quantity in said atleast one air-suspension bellows by placing said at least oneair-suspension bellows in communication with said suction port of saidcompressed-air delivery device and said outlet port of saidcompressed-air delivery device in communication with said compressed-airaccumulator, said changeover-valve device being piloted with compressedair of said air-suspension system.
 2. The air-suspension systemaccording to claim 1, wherein said changeover-valve device includes apilot valve and a changeover valve.
 3. The air-suspension systemaccording to claim 2, wherein said changeover valve a 4/2-way valve thatis actuatable by compressed air.
 4. The air-suspension system accordingto claim 2, wherein said pilot valve is an electrically actuatable3/2-way valve.
 5. The air-suspension system according to claim 2,wherein said changeover valve includes two 3/2-way valves that are bothactuatable by said pilot valve by means of compressed air.
 6. Theair-suspension system according to claim 1, wherein saidchangeover-valve device includes at least one electromagnet.
 7. Theair-suspension system according to claim 1, wherein pilot pressure forsaid changeover-valve device is drawn from an outlet side of saidcompressed-air delivery device.
 8. The air-suspension system accordingto claim 1, wherein pilot pressure is discharged to atmosphere when saidchangeover-valve device is switched between said first and second valvepositions.
 9. The air-suspension system according to claim 1, furthercomprising a check valve (52), for bypassing said compressed-airdelivery device, said check valve being connected to ports of saidchangeover-valve device in communication with said compressed-airdelivery device.